EDITORS PLEASE NOTE: CONTAINS GRAPHIC MATERIAL
Fifteen lives have been added to the Palestinian death toll that has now risen above 750.
Gazan authorities say Israeli forces bombed a shelter at a U.N.-run school, Thursday.
The Health Ministry says an additional 200 people were wounded in the attack.
The Israeli military had no immediate comment.
Pools of blood lay on the ground, while victims were frantically transported to various medical centers.
(SOUNDBITE) (English) UNRWA SPOKESMAN CHRISTOPHER GUNNESS, SAYING:
"We again say enough civilians, enough women, enough children. They have suffered quite enough in this appalling conflict. It must end and thereafter there must be serious engagement with dealing with the underlining causes of the conflict in Gaza."
Despite attempts at mediation, a truce between Israel and Hamas militants remains elusive.
Deputy spokesman for Ban Ki-Moon says the UN is appalled by the attack:
(SOUNDBITE) (English) DEPUTY SPOKESMAN FOR THE SECRETARY GENERAL FARHAN HAQ SAYING:
"He once again says all sides must abide by their obligations under international and humanitarian law to respect the sanctity of civilian life, inviolability of U.N. premises and to honor their obligations to humanitarian workers. Today's attack underscores the imperative for the killing to stop and to stop now."
More than 140,000 Palestinians have fled 17 days of fighting -- many of them seeking shelter in buildings like these.

Reuters is the news and media division of Thomson Reuters. Thomson Reuters is the world's largest international multimedia news agency, providing investing news, world news, business news, technology news, headline news, small business news, news alerts, personal finance, stock market, and mutual funds information available on Reuters.com, video, mobile, and interactive television platforms. Learn more about Thomson Reuters products: